Currently various types of industrial handlers are known to be used in a broad range of applications. For example, it is common to use robots and other handlers on press lines used to manufacture vehicle bodywork parts. The industrial handlers are used to carry out tasks such as loading and unloading the parts between one press and another, or a store room and a press, conveyor belt and a press etc.
One type of handler which is frequently used because of its ability to adapt to a great variety of different movements and cycles, is articulated robots, for example robots with four or six degrees of freedom; each degree of freedom is an independent movement (turn or displacement) that one articulation can make with respect to the preceding one. Another type of handler used on press lines are the so-called “Doppins”, which generally consist of a structure attached to the press and equipped with a guide on which a cart travels vertically; the cart is fitted with a system of articulated arms, which is responsible for the movement of entering and exiting the press for loading or unloading parts.
On all handlers, an end element is installed on the system's free end, which in the case of press automation is a gripping element adapted to the parts to be loaded and unloaded; this gripping element is usually called a “gripper”, and can use either a mechanical, electromagnetic or vacuum gripping system, depending on each case's specific requirements.
There may be different handling configurations between one station and another of a press line: for example, a single handler that extracts the part from one station and introduces it into another one, or a pair of handlers, one for unloading from one station and another one for loading it onto the following station, with or without the interposition of conveyor belts, rotary mechanisms, etc.
In most cases, on press lines, as in most industrial operations, it is advisable to minimise cycle times; where handlers are concerned, an important part of the cycle is the extraction or insertion of the part in relation to the press's area of influence, since during this phase the press must remain open, and therefore, inactive; consequently, it is advisable to extract and insert the part quickly.
What follows is a discussion of this problem, by way of example, with reference to an articulated robot that extracts a part from one press and inserts it into the following one. There are basically two cycles that an articulated six-axis robot, with a gripper attached to its sixth axis, can perform for this operation. In one cycle, usually called the “external” cycle, the robot first extracts the gripper holding the part from the press following a rectilinear trajectory in parallel to the press line, through combined turns around the first three axes; secondly, it makes the gripper turn with regard to the 4th and 6th axes to leave it facing the following press; and finally, it inserts the part into the press following a rectilinear trajectory.
The advantage of this type of cycle is that the partial extraction and insertion times are relatively short, because the movements are linear; however, the overall cycle time is fairly long. In an alternative cycle, usually called an “internal” cycle, which can be seen in FIG. 1, the robot maintains its arm extended and through simultaneous turns with regard to the 1st and 6th axes makes the gripper with the part perform a single movement with a trajectory, essentially horizontal, which occurs between the 6th axis and the base of the robot; however, due to the rotation around the 6th axis, the part turns during the extraction and the insertion in the presses.
The overall cycle time in this case is relatively small, due to the fact that the robot performs a single movement; however, the partial extraction and insertion times for the parts are high, because the part's turn makes a section of it remain longer under the press. Another inconvenience of turning the part during the extraction and the insertion in the presses is that the obstacles represented by the press columns themselves must be taken into account, which can make the gripper's turning with the part difficult.
Thus conventional solutions for loading and unloading from presses present limitations when it comes to in reducing cycle times. Moreover, in both cases, the part is turned 180° when passing from one press to another. FIG. 3 (prior art) shows such a known method. The figure shows a robot R which transfers a part from a first press to a second press. Rotation of the part around the robot sixth axis enables the part to be inserted in the second press, but the part has to be turned through 180° in order to do this.
In recent years, some devices or accessories have been proposed intended to be coupled with the 6th axis of an articulated robot, which partially resolve these problems. European patent application EP666150A1, entitled Wrist structure for articulated robots, assigned to Yaskawa, describes a mechanism that is coupled to the robot's wrist and displaces the turn of the 6th axis to the end of a rigid bar. This mechanism makes it possible to maintain the part's orientation as it passes from one press to another, and makes a linear extraction and insertion movement; however, the robot is forced to retract considerably for this movement, which makes it fairly slow, especially if the distance between presses is large. Another inconvenience of this mechanism is that, due to the fact that there is no possibility of turn around the robot's 6th axis, to enter the press laterally the bar must be fairly long, and this causes problems of weight, rigidity and similar.
Another known device includes two bars articulated to each other by their ends; a first bar is coupled by its other end to the robot's 6th axis, while the other end of the second bar is coupled to the gripper for the part to be handled. There is a motor on the articulation between the two bars, which makes it possible to action the gripper's rotation in relation to the second bar. This system makes it possible to transfer the part with an internal turn, such as the one represented in FIG. 1, but with linear extraction and insertion into the presses, since the combination of rotations around the different axes makes it possible to rotate the gripper holding the part in the opposite sense to the robot arm's turn during the phases of extraction or insertion, thus maintaining the part's orientation, and performing an approximately linear movement between one press and another. Nonetheless, this system is relatively complex, because it implies two bars articulated to each other, with the ensuing inconveniences concerning the assembly's rigidity.
At the same time, and irrespective of the robot's movements, it is also advisable to ensure that the gripper is of limited height, in order to be able to partially overlap the press's opening and closing movements with the part's insertion and extraction; and it is also desirable, in terms of safety and savings, that the gripper and any other part of the handler which penetrates within the press's area of influence are made of light low-hardness materials, compatible with their function, in order to minimise as much as possible any damage to the press in the event of an accident. In the described system with two articulated bars, the rigidity requirements make it difficult to reduce the height of the assembly; moreover, the articulation with the motor penetrates within the press's area of influence, with the consequent risk of significant damage in the event of an accident.
An industrial handler is disclosed in WO2006/018459, entitled Part-handling device and industrial handler comprising said device, to ABB, which describes a device intended to be coupled to an industrial handler that presents a kinetic chain between a base and an end element. The device comprises: a rigid arm, which is designed to be linked to the handler's end element; a support which is mounted to the rigid arm so that it can move and which is designed to be rigidly coupled to an element for gripping the parts to be handled; and a motor or other means for actuating the movement of the support in relation to the arm. The part is turned through 180° before entering the second or following press.